PROJECT SUMMARY/ABSTRACT The long term goal of this research is to understand how the ability to use talker voice characteristics to understand speech in multitalker environments develops from childhood to adulthood. The proposed research is designed to characterize the way children are able to utilize acoustic voice cues to separate competing speech in multitalker environments. It is well established that children are more susceptible to competing speech sounds compared to adults and emerging evidence suggests this can have a detrimental impact on learning. In multitalker environments, children?s speech-in-speech understanding can often improve by utilizing the same sound segregation cues as adults. For example, children can benefit from a sex mismatch between competing talkers but the relative contribution of the individual voice characteristics to this benefit is unknown. In this study, we will investigate children?s ability to benefit from talker differences in fundamental frequency (F0) and vocal tract length (VTL), the two primary voice characteristics that differentiate male and female voices. The overall goal of the proposed research is 1) To evaluate the independent effects of target/masker voice differences in F0 and VTL on children?s ability to segregate target from masker speech, and 2) To determine when the ability to benefit from combined differences in vocal characteristics between target and masker speech matures in children. The central hypothesis is that the ability to use differences in voice characteristics to separate target from masker speech follows a protracted pattern of development, and that children will derive less benefit when cues are presented in isolation than when these cues are combined. This central hypothesis will be tested by first isolating F0 and VTL to see their independent influence on speech-in-speech understanding. These two cues will then be combined in order to determine whether cue redundancy could reduce the child/adult differences that are observed in these contexts. Previous research has demonstrated that adults are able to benefit from these two cues and that this benefit extends to adults with hearing loss who wear hearing aids. The findings from the proposed research are expected to lead to a more complete understanding of how acoustic voice characteristics contribute to children?s speech-in-speech understanding and will pave the way for the development of intervention strategies for children with hearing loss.